The present invention relates to an angular velocity sensor which can be employed in various control systems, such as a vehicle motion/behavior control system as well as a navigation system, or in a video camera for compensating the operator""s hand movement, and more particularly to an angular velocity sensor which detects an angular velocity using a piezoelectric vibrator.
Japanese Unexamined Patent Application No. 8-210860, published in 1996, discloses a conventional angular velocity sensor which comprises a piezoelectric vibrator configured into a tuning fork with a pair of arm bars and a connecting bar. According to this angular velocity sensor, the vibrator causes a predetermined vibration in a driving direction along which the arm bars are arrayed. When the sensor is subjected to an angular velocity, a Coriolis force derived from the angular velocity is detected as a vibration change of the vibrator caused in a sensing direction normal to the driving direction.
Japanese Unexamined Utility Application No. 5-71715, published in 1993, discloses another angular velocity sensor employing a lead wire arrangement according to which terminals of lead wires are located adjacent to a vibrator to shorten the length of each lead wire in the air.
An object of the present invention is to provide a novel, accurate and reliable angular velocity sensor.
Another object of the present invention is to provide a manufacturing method for fabricating this angular sensor.
Another object of the present invention is to provide a piezoelectric vibrator element used in this angular sensor.
In order to accomplish the above-described and other related objects, one aspect of the present invention provides an angular velocity sensor with a vibrator. The vibrator comprises a piezoelectric body configured into a predetermined shape having at least one pair of arm bars and a connecting bar. Electrodes are formed on an outer surface of the piezoelectric body. At least one drive electrode receives an alternating voltage to vibrate the arm bars in a drive axis direction along which the arm bars are arrayed. At least one sensing electrode detects a vibration caused in a sensing axis direction normal to the drive axis direction. The outer surface of the piezoelectric body comprises a front face and a rear face both being U-shaped. The drive electrode and the sensing electrode are formed on the front face, while a first reference electrode having a predetermined reference potential is formed on the rear face. At least one second reference electrode is formed on at least one side face of the aim bars of the piezoelectric body at a position corresponding to the sensing electrode. The second reference electrode is connected to the first reference electrode formed on the rear face.
Preferably, at least one additional sensing electrode is formed on the rear face at a predetermined arm portion corresponding to the sensing electrode, and at least one short-circuit electrode is formed on the side face of the arm bars to connect the additional sensing electrode to the sensing electrode.
Preferably, at least one ground electrode is formed on the front face at a predetermined position of the arm bars, and at least one short-circuit electrode is formed on the side face to connect the ground electrode to the first reference electrode.
Preferably, at least one monitor electrode is formed on the front face at a predetermined position of the arm bars, and the monitor electrode detects a vibration caused in the drive axis direction.
Preferably, the piezoelectric body is polarized from the front face to the rear face or vice versa by applying a predetermined voltage between the electrodes formed on the front and rear faces, and the electrodes formed on the side faces of the arm bars are fabricated after finishing the polarization of the piezoelectric body.
Preferably, the electrodes formed on the side faces of the arm bars are made of a low-temperature hardening type conductive resin.
Preferably, metallic wires are wire bonded to the electrodes formed on the front face of the piezoelectric body.
Preferably, a bonding position of a metallic wire connected to the sensing electrode formed on the front face is offset toward the connecting bar.
Preferably, the vibrator is secured to a base member, and the metallic wires are connected to terminals provided on the base member for inputting and outputting signals.
Another aspect of the present invention provides a manufacturing method for an angular velocity sensor. According to this manufacturing method, a first step is performed for forming the drive electrode and at least one polarizing electrode on a U-shaped front face of the piezoelectric body, and for forming a common electrode on a U-shaped rear face at a region corresponding to the drive electrode and the polarizing electrode. The polarizing electrode is positioned closer to a distal end of a corresponding arm bar than the drive electrode. Succeeding to the first step, a second step is performed for polarizing the piezoelectric body by applying a predetermined polarization voltage between the common electrode formed on the rear face and the electrode formed on the front face. Then, succeeding to the second step, a third step is performed for forming the sensing electrode on at least one side face of the piezoelectric body at a predetermined arm portion corresponding to the polarizing electrode.
Preferably, the first step includes a formation of at least one monitor electrode on the front face for monitoring a vibrating condition of a corresponding arm bar in the drive axis direction, so that the monitor electrode is interposed between the polarizing electrode and the drive electrode. The second step includes an application of the polarization voltage between the monitor electrode and the common electrode for polarizing the piezoelectric body.
Preferably, the first step includes a formation of at least one pad electrode on the front face for outputting a detection signal. The third step includes a formation of at least one lead electrode on at least one side face for connecting the sensing electrode and the pad electrode.
Preferably, the pad electrode is formed at a predetermined arm portion closer to a distal end of a corresponding arm bar than the polarizing electrode or at a predetermined arm portion closer to the connecting bar than the polarizing electrode.
Preferably, the first step includes a formation of at least one ground electrode on the front face for connecting the common electrode to a reference potential. The third step includes a formation of at least one short-circuit electrode on at least one side face for connecting the common electrode to the ground electrode.
Preferably, a processing temperature for the electrode formed on the side face in the third step is lower than a Curie temperature of the piezoelectric body.
Preferably, a conductive resin, hardening at a temperature lower than the Curie temperature of the piezoelectric body, is used for the formation of the electrode formed on the side face in the third step.
Preferably, a metallic deposition is used for forming the electrode on the side face in the third step.
Another aspect of the present invention provides an angular velocity sensor with a vibrator, a base plate and a supporter interposed between the vibrator and the base plate. The vibrator comprising a piezoelectric body having at least one polygonal arm bar and electrodes formed on the piezoelectric body. The electrodes include at least one drive electrode, at least one outlet electrode and at least one sensing electrode formed on a first face of the piezoelectric body, and a common electrode formed on an opposing second face of the piezoelectric body. The common electrode is integrally connected to the outlet electrode on the first face. The base plate confronts with the second face. The supporter supports the vibrator to the base plate. The piezoelectric body is polarized in an X-axis direction from the first face to the second face. The arm bar vibrates in a Y-axis direction parallel to the first and second faces and normal to a longitudinal direction of the arm bar, when an alternating voltage is applied between the drive electrode and the common electrode. The sensing electrode produces a signal representing a vibration of the arm bar caused in the X-axis direction due to an angular velocity of the vibrator appearing about a predetermined axis. The base plate has a reference face opposing to the second face of the vibrator. The reference face is provided with terminals electrically connected to the electrodes formed on the piezoelectric body. At least one of the drive electrode, the sensing electrode and the outlet electrode is connected to a corresponding one of the terminals via a lead wire chiefly made of aluminum by ultrasonic wire bonding.
In this case, the reference face may be provided with at least one hybrid IC substrate and at least one terminal electrically connected to the hybrid IC substrates. And, at least one of the drive electrode, the sensing electrode and the outlet electrode is connected to the hybrid IC substrate via a lead wire chiefly made of aluminum by ultrasonic wire bonding.
Preferably, the lead wire contains aluminum by a percentage equal to or larger than 90%.
Preferably, the vibrator is configured into a tuning fork with bifurcated arm bars causing a vibration and a connecting bar connecting base ends of the bifurcated arm bars. The first and second faces are opposing U-shaped flush surfaces extending along the arm bars and the connecting bar. The supporter supports a center of the connecting bar.
Preferably, the supporter has a neck portion extending in parallel to a longitudinal direction of the arm bars.
Preferably, the lead wire has a diameter equal to or smaller than 50 xcexcm, or in a range of 30 xcexcm to 50 xcexcm, or a value capable of suppressing a temperature drift of the vibrator equal to or less than 10xc2x0/sec.
Preferably, the lead wire has a staring point and an ending point for the ultrasonic wire binding. The starting point is positioned farther than the ending point in the X-axis direction with respect to the reference face of the base plate.
Preferably, the lead wire is configured into a loop shape protruding from the first face of the vibrator and the reference face of the base plate between the starting point and the ending point, with a wire height equal to or larger than 0.4 mm as a clearance between the first point and a top of the lead wire in the X-axis direction. The wire heigh is equal to or smaller than 1.2 mm.
Preferably, the lead wire is arranged at a bonding angle xcex8 in a range of 0-60xc2x0, when the bonding angle xcex8 is an angle between the lead wire and the Y-axis direction when seen from the X-axis direction.
Another aspect of the present invention provides a manufacturing method for an angular velocity sensor with a vibrator comprising a piezoelectric body having at least one polygonal arm bar extending is a Z-axis direction. The piezoelectric body has a first face on which at least one drive electrode and at least one pad sensing electrode are formed. The drive electrode causes the arm bar to vibrate in a Y-axis direction normal to the Z-axis direction. The pad sensing electrode outputs a detection signal. The piezoelectric body has at least one second face neighboring to the first face. The second face is provided with at least one angular velocity sensing electrode and at least one lead electrode. The angular velocity sensing electrode detects a vibration of the arm bar caused in an X-axis direction normal to both of the Y-axis and Z-axis directions. The lead electrode connects the angular velocity sensing electrode to the pad sensing electrode. For manufacturing this angular velocity sensor, the manufacturing method comprises a first step for forming a predetermined pattern of electrode film on one face of a piezoelectric plate by printing and sintering. Next, a second step is performed for cutting the piezoelectric plate together with the electrode film so as to leave at least one cut surface serving as the second face, thereby forming the first and second faces with the drive electrode and the pad sensing electrode. Then, a third step is performed for forming the angular velocity sensing electrode and the lead electrode on the second face, wherein a printing operation of the lead electrode is performed prior to a hardening operation of the lead electrode so that a print sagging of the lead electrode extends over a comer ridgeline of the arm bar and overlaps with the pad sensing electrode formed on the first face.
Alternatively, for manufacturing the angular velocity sensor, the manufacturing method may perform a first step for cutting a piezoelectric body into a shape of the vibrator while leaving at least one cut surface at a side thereof. Then, a second step is performed for forming the drive electrode and the pad sensing electrode on the first face by printing and sintering. Furthermore, a third step is performed for polishing the cut surface of the piezoelectric body by a predetermined thickness so as to form the second face. Then, a fourth step is performed for forming the angular velocity sensing electrode and the lead electrode on the second face, wherein a printing operation of the lead electrode is performed prior to a hardening operation of the lead electrode so that a print sagging of the lead electrode extends over a comer ridgeline of the arm bar and overlaps with the pad sensing electrode formed on the first face.
Preferably, a polarizing step is performed, prior to the step for forming the angular velocity sensing electrode and the lead electrode, by applying a DC voltage to the piezoelectric body constituting the vibrator so that the piezoelectric body is polarized in a predetermined direction. A resinated conductor contaning metallic particles in a resin is used in the step for forming the angular velocity sensing electrode and the lead electrode, wherein the resinated conductor is printed on the second face in a pattern corresponding to the angular velocity sensing electrode and the lead electrode and then hardened at a temperature lower than a Curie temperature of the piezoelectric body.
Preferably, the resinated conductor comprises metallic particles configured into balls and flakes.
Preferably, the lead electrode is formed so as to have a widened portion at the comer ridgeline.
Another aspect of the present invention provides an angular velocity sensor with a vibrator comprising a piezoelectric body having at least one polygonal arm bar extending is a Z-axis direction. The piezoelectric body has a first face and a second face neighboring to the first face. At least one first electrode and at least one pad electrode are formed on the first face. At least one second electrode and at least one lead electrode are formed on the second face, so as to cause the arm bar to vibrate in a Y-axis direction normal to the Z-axis direction and output a detection signal representing a vibration of the arm bar caused in an X-axis direction normal to both of the Y-axis and Z-axis directions. The pad electrode and the lead electrode extend over a comer ridgeline to a neighboring face each other so as to form an overlapped connecting portion.
Preferably, the first electrode is at least one drive electrode and the second electrode is at least one angular velocity sensing electrode.
Preferably, the angular velocity sensing electrode and the connecting electrode formed on the second face are made of a resinated conductor comprising metallic particles mixed in a resin, and the resinated conductor is hardened at a temperature lower than a Curie temperature of the piezoelectric body. The resinated conductor may comprise metallic particles configured into balls and flakes. The connecting electrode may have a widened portion at the comer ridgeline. The overlapped connecting portion has a first overlap length extending in the X-axis direction from the comer ridgeline and a second overlap length extending in the Y-axis direction from the comer ridgeline. The first overlap length and the second overlap length are equal to or larger than 20 xcexcm. The arm bar is chamferred along the comer ridgeline.
Preferably, the vibrator is configured into a tuning fork with bifurcated arm bars and a connecting bar connecting base ends of the bifurcated arm bars. The first face and the third face are opposing flush faces extending the arm bars and the connecting bar. The X-axis direction in normal to the first face and the third face, while the arm bars are arrayed along the Y-axis direction.
In the above-described angular velocity sensor, the piezoelectric body may have a third face in addition to the first and the second faces. The third face opposes to the first face. A common electrode is formed on the third face, so as to cause the arm bar to vibrate in a Y-axis direction normal to the Z-axis direction by applying an alternating voltage between the first electrode and the common electrode and output a detection signal through the angular velocity sensing electrode as a signal representing a vibration of the arm bar caused in an X-axis direction normal to both of the Y-axis and Z-axis directions. The connecting electrode may be formed on the second face for providing an electrical connection to the electrodes formed on the third face. And, the connecting electrode and the electrodes formed on the third face extend over a corner ridgeline to a neighboring face each other so as to form an overlapped connecting portion.
To manufacture the above-described angular velocity sensor, a manufacturing method is provided, according to which a first step is performed for cutting a piezoelectric plate into a shape of the vibrator so as to leave at least one cut surface serving as the second face. A second step is performed for forming the first electrode and the pad electrode on the first face, so that a first print sagging of the pad electrode extends over a corner ridge of the arm bar to the second face. Then, a third step is performed for forming the second electrode and the lead electrode on the second face, so that a second print sagging of the lead electrode extends over the corner ridge of the arm bar to the first face, thereby forming an overlapped connecting portion of the first print sagging and the second print sagging in a vicinity of the corner ridgeline.
The manufacturing method may comprise the second step for forming the drive electrode and the pad electrode on the first face and forming the common electrode on the third face, so that a first print sagging of at least one of the pad electrode and the common electrode extending over a corner ridge of the arm bar to the second face. A polarizing step may be performed after the second step to polarize the piezoelectric body in a predetermined direction by applying a DC voltage. The third step may be performed for forming the angular velocity sensing electrode and the connecting electrode on the second face, so that a second print sagging of the connecting electrode extending over the comer ridge of the arm bar to at least one of the first face and the third face, thereby forming an overlapped connecting portion of the first print sagging and the second print sagging in a vicinity of the comer ridgeline.
Preferably, the angular velocity sensing electrode, the connecting electrode and the second sagging are formed by printing a resinated conductor on the second face, and the resinated conductor comprises metallic particles mixed in a resin and is hardened at a temperature lower than a Curie temperature of the piezoelectric body.
Another aspect of the present invention provides a piezoelectric vibrator element comprising a piezoelectric vibrator member, at least one electrode formed on the vibrator member, and at least one lead wire bonded to the electrode. The lead wire contains aluminum as a chief component and is bonded to the electrode by ultrasonic wire bonding. The electrode is a silver thick film containing palladium.
Preferably, the lead wire has a diameter equal to or smaller than 50 xcexcm. The electrode has a film thickness in a range of 10 xcexcm to 40 xcexcm. At least one first-layer electrode is formed on a face of the vibrator member and at least one second-layer electrode is formed on the first-layer electrode so as to constitute a double-layer construction. The lead wire is bonded on the second-layer electrode. The second-layer electrode contains palladium by an amount in a range of 5% to 50% as a weight percentage relative to a total amount of the silver and the palladium. The first-layer electrode contains glass or inorganic oxide by an amount in a range of 1% to 15% as a weight percentage relative to a total amount of the first-layer electrode. The second-layer electrode contains glass or inorganic oxide by an amount smaller than 1% as a weight percentage relative to a total amount of the second-layer electrode.
Preferably, the electrode and the piezoelectric vibrator member are exposed to a nitrogen atmosphere.